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07-16-2013 05:51 PM
If it seems too good to be true, it probably is.
Recently I purchased a 64GB microSD card through a marketplace I use often that was said to be from a major manufacturer for a very good but reasonable price (about 2X what a 32 GB costs instead of 2.5X) and in an original appearing package. On first connection it gave errors and seemed slow. I reformatted it but still seemed wrong.
Called the manufacturer and the numbers on the chip did not match a good one. Ran the bar code on the back and it came back as a much different device.
Apparently this is not a new situation and for more than you ever wanted to know including a utility to check see http://sosfakeflash.wordpress.com/.
What appears to be being done is to rewrite the SD Card partition table to change the number and ending sector to make a card "appear" larger. In my case it appears to be an 8GB card remarked as a 64 GB card. And a slow one (~4 MB/s write) at that.
The card may act normally for the first use of the drive up to its actual size but addresses beyond that limit may wrap back to the start and overwrite not just the original data but also the critical device information so that the next time it is loaded the device will be corrupt & all data lost.
Just to be clear, this is not an Acer issue, it related to microSD cards purchased elsewhere for use in our devices that you may encounter in the marketplace so be aware and know how to validate (either call the manufacturer with the numbers or run a fulll test).
07-16-2013 06:39 PM - edited 07-16-2013 06:44 PM
I always use Class 10 from SanDisk. Never with noname or from eBay.
Any problem with 16, 32 or 64 Go. Some are in FAT32, NTFS or ext4. No data lost, no error.
Use on HTC phone, Galaxy phone, Asus TF300T tablet (2 x 32), Acer W510, Nikon and Canon camera.
In France a 32 Go micro SDHC Class 10 SanDisk with adapter cost around 50 $ (and 70 $ for a 64 Go).
The Bible for SD Card: Wikipedia Secure Digital
07-16-2013 08:21 PM
This appered to be in a retail pack from an equally reputable manufacturer as SanDisk. All markings appeared correct until I called to verify.
BTW one sign that may show up in disk properties is a 64GB disk that reports over 64,000,000,000 bytes.
07-16-2013 10:04 PM - edited 07-16-2013 10:07 PM
62.4 * 1.024 = 63.897 Count is almost right.
It would actually be:
62.4 * 1024 * 1024 * 1024 = 67001489817.6 for gigabytes.
Or more accurately yet:
67,106,762,752 /1024 / 1024 / 1024 = 62.49804306030273 ~ 62.4 (though I would have rounded it up to 63.5 myself)
07-16-2013 11:41 PM - edited 07-16-2013 11:53 PM
True except that since the daze of the IBM-PC (1981-), a megabyte has been a million bytes (1,000,000) and not the hexadecimal 1,000h (1,048,576). Blame it on the marketeers if you will. MaxStor used to print it on the hard drive boxes.
See http://en.wikipedia.org/wiki/Megabyte (section under Base 10)
Also what you see under Windows "properties" for a drive is the logical volume data and not the physical disk data. Try playing around with the program DISKPART.EXE (unless you really know what you are doing use only the LIST and SELECT commands).
For example when I list the partitions on a 2GB micro SD (was handy), it shows the disk as 1898 MB with one partition (what Windows sees) of 1897MB (Windows says 1.85GB or 1,989.869,568 bytes) with an offset of 65 kb. The difference is in the Marketting definition and the computer definition of a MegaByte.
Now that 65 KB offset contains the master boot record, the partition table(s), and the File Allocation Tables. If you format NTFS insead of FAT it takes more. This never shows up in the Windows "properties" pie chart.
So I can garuntee you that if the Capacity: bytes reported by Windoze is more than 64,000,000,000 bytes for a 64GB drive, somebody is being creative
07-17-2013 03:19 AM
Actually, that 'kilo equals a thousand, mega equals a million' thing has only been there as a marketing ploy for hard drive manufacturers. Programmers have always used the 'powers of two' model. Remember floppy disks? They tended to use 512 byte sectors and a 720k floppy held 1440 sectors, a 1.44M floppy had 2880 sectors (and if you were an Amiga fan an 880K floppy had 1760 sectors and a 1.76M floppy had 3120 sectors). System memory has been modeled as programmers like as well, where kilo is 1024, mega is 1024*1024, etc...
07-19-2013 03:05 PM
Hve to understand that back when a 10 MB ST512 was $3,000 every byte was important so the larger a number the drive mfr could put on a box the better.
Yes, computers and programmers think in Hex and can count to over a thousand on their fingers. Instructions in hex would fall out in logical arrays. Once upon a time microcode was important and you could do anything with cascaded bit slice processors like the AMD 2901.
But the "great unwashed" neever understood the difference so when consumer hard drives came out a standard was developed that had big numbers to help justify the big prices.